Recovery of tin from slags

ABSTRACT

A method of producing tin from a low grade tin concentrate comprising the following steps: 1. Melting and partial reduction of the mixture of concentrate and flux, to form a liquid concentrate slag (i) having a high tin content; 2. Mixing and reacting the liquid concentrate slag (i) with a liquid tin-iron alloy (hard-head) (ii)) having a high iron content to yield a liquid crude tin metal product (iii) of low iron content and a liquid intermediate slag (iv) of high tin content. 3. Reduction of the tin in the liquid intermediate slag (iv) resulting from step (2) to produce liquid tin-iron alloy (ii) for recycle to step (2) and a liquid discard slag (v) of low tin content. The process may be operated either continuously or batchwise.

[451 Sept. 16, 1975 1 1 RECOVERY OF TIN FROM SLAGS John Millice Floyd,Glen Waverley, Australia [75] lnventor:

' [73] Assignee: Commonwealth Scientific and Industrial ResearchOrganization, Campbell, Australia [22] Filed: Aug. 22, 1974 [21] Appl.No.: 499,644

Related U.S. Application Data [63] Continuation-impart of Ser. No.276,052, July 28,

1972, abandoned.

[30] Foreign Application Priority Data July 30, 1971 Australia 5733/71[52] U.S. Cl. 75/85; 75/89; 75/93 [51] Int. Cl. C22B 25/00 [58] Field ofSearch 75/85, 89, 91, 93, 72, 75/12; 266/34 C [56] References CitedUNITED STATES PATENTS 2,663,631 12/1953 Tschop et a1. .1 75/91 2,673,7973/1954 Whitehouse et a1. 75/91 2,815,267 12/1957 Platteeuw et a1. l75/85 2,849,860 9/1958 Lowe 266/34 C 3,201,104 8/1965 Berry 266/34 C3,575,706 4/1971 Ummel 266/34 C 3,634,069 1/1972 Worner 75/85 3,674,4637/ 1972 Yannopoulos 75/72 FOREIGN PATENTS OR APPLICATIONS 17,002 7/ 1906United Kingdom 75/85 401,372 5/1969 Australia 75/12 PrimaryExaminer-Walter R. Satterfield Attorney, Agent, or F irm-Cushman, Darby& Cushman 5 7 ABSTRACT A method of producing tin from a low grade tinconcentrate comprising the following steps:

1. Melting and partial reduction of the mixture of concentrate and flux,to form a liquid concentrate slag (i) The process may be operated eithercontinuously or batchwise.

10 Claims, No Drawings RECOVERY OF TIN FROM SLAGS This invention is acontinuation in part of U5. Ser. No. 276,052 filed July 28, 1972 and nowabandoned.

This invention relates to the smelting of tin concentrates using aprocess involving the gaseous reduction of liquid slags containing tin.The invention has particular relevance to the smelting of low grade tinconcentrates.

Conventional methods of tin extraction are concerned with the treatmentof high grade tin concentrates. The mineral beneficiation of alluvialtin deposits to tin rich concentrates with greater than 60% tin iscomparatively simple, and does not result in a great loss of tin intailings. Hard rock tin deposits, on the other hand, can usually only beconcentrated to these levels with the loss of over half of tin contentof the ore. The production of lower grade concentrates from hard rockdeposits results in lower tin losses, so that if this material can besmelted economically, then a considerable saving in tin can result.

Tin mining has traditionally been concerned with alluvial deposits, butproduction from these deposits has been unable to produce enough tin forrising world consumption, and an increasing proportion of the total tinoutput is produced from hard rock deposits.

In the conventional process for tin smelting tin concentrates containinggreater than 60 percent tin, mixed with a solid reductant, such as coal,and a flux, such as limestone to produce a fluid slag, are smelted in areverberatory furnace at a temperature of about I200C.

' A crude tin is produced for refining, and a slag with a in areverberatory furnace. In the slag smelt the temperature is raised toabout 1400". A tin metal of high iron content (hard-head) is produced,and is charged with concentrate to the first smelting stage. Theresulting slag contains 1.5 to 3 percent tin and is discarded. Thisprocess cannot be economically used for smelting low grade concentratesbecause of the necessity of cooling and reheating large quantities ofslag. Reduction of tin from the slag requires intimate contact betweenreductant and slag, and with a solid carbonaceous reductant this canonly be achieved by cooling,

mixing with reductant and reheating to much higher temperatures thanused in the method described in this invention.

Low grade tin concentrates in general possess a higher iron to tin ratiothan high grade tin concentrates.

During the reduction of tin from the oxide to the metal wt. 71 Fe inslag wt 7: Sn in slag wt. 7! Sn in metal wt. 7; Fe in metal The value ofis strongly dependent on the iron content of the metal. The distributioncoefficient for the first stage of conventional smelting with metalcontaining less than 2 wt. Fe, has a value in the range to 400, whilethe second stage distribution coefficient, has a value in the range 20to 50 for iron contents in the metal of 20 to 60 wt. Fe.

Low grade concentrates are at present smelted in a blast furnace whereconditions are normally strongly reducing so that a large proportion ofthe iron in the charge reports in the metal. If metal with a low ironcontent is required from the blast furnace then a low iron contentcharge is selected and a light reduction is used to produce a' slag withhigh tin content for further treatment. For example if a metal with 2percent iron is required assuming a 2 value of 200, the ratio of iron totin in the slag cannot be greater than about 4. Normally a metal withhigh iron is produced, and this is then subjected to treatments forremoval of iron which entail production of more tin-rich material forfurther treatment. The complete process sequence for blast furnaceoperation may be quite complicated.

In some recently developed processes the slag from the slag smelt issubjected to a fuming operation, similar to that used for zinc recoveryfrom lead blast furnace slag. In the fuming process for tin, air, withentrained fine carbonaceous reductant such as crushed coal, andentrained sulphidising agent such as pyrites, is blown into the liquidslag. Volatile tin sulphide is formed, removed by the entraining gas,and reacts with oxygen above the slag bath to produce a fume of SnO Thefume is filtered from the gas and charged to a reverberatory furnacesmelt. The slag after fuming contains 0.1 to 0.5 percent tin.

A method of smelting low grade tin concentrates was proposed inAustralian Patent Application 10581/66 and involved the use of a rotaryfurnace in a two stage countercurrent process. In the first stageconcentrate, flux, iron-tin alloy, and possible solid carbonaceousreductants were smelted to produce a crude tin for refining, which wastapped fromthe furnace, and a slag with a high tin content. Solidcarbonaceous reductant and flux were to be added to the molten slag andsmelted in the second stage to produce a low tin content slag, which wasto be tapped from the furnace, and an irontin metal which was to haveremained in the furnace, for the first stage to be repeated. In thefirst stage the iron in the metal acts as a reducing agent for the tinin the concentrate but, if desired, additions of carbonaceous reductantcould be made. the process was not exploited commercially because thesecond stage did not produce a significant quantity of hard-head or aslag of low enough tin content for discarding, in full scale trials.

There were two principal reasons why the process failed in the secondstage. Firstly the addition of carbonaceous reductant to the liquid slagresulted in the reductant floating on the slag surface, so that goodcontact between reductant and slag was not achieved. Secondly commercialrotary furnaces cannot achieve temperatures above 1300C, and it has beenfound that temperatures greater than 1350C are required for effectivereduction of tin slags by carbonaceous reductants.

We have now shown that both of these factors can be overcome byinjecting a reducing gas into the slag due to the very differentphysical situation thereby produced. The bubbles of reductant provide arelatively large contact area, and in rising to the surface they mix theslag, thus improving rates of mass transfer so that the reduction iseffective at lower temperatures.

The present invention involves a process for the smelting of low gradetin concentrates which in essence involves the following three steps:

1. Melting and partial reduction of the mixture of concentrate and flux,to form a liquid concentrate slag (i) having a high tin content 50% Sn);

2. Mixing and reacting the liquid concentrate slag (i) with a liquidtin-iron alloy (hard-head) (ii) having a high iron content l0 60% Fe) toyield a liquid crude tin metal product (iii) of low iron content (0.1 2%Fe) and a liquid intermediate slag (iv) of high tin content (lO 40% Sn).This reaction may be achieved by mixing of the liquid phases resultingfrom the injection of gases, or combustion mixtures of fuel and air suchas will produce reducing gases, or by use of a rotary furnace. The metalproduct (iii) and the intermediate slag (iv) are then separated.

3. Reductionof the tin in the liquid intermediate slag ,(iv) resultingfrom step (2) to produce liquid tin-iron alloy (ii) for recycle to step(2), and a liquid discard slag (v) of low tin content (0.5 2% Sn). Thisreduction is carried out by injecting reducing gases (which may containentrained solid carbonaceous reductants) or reducing mixtures of fueland air and/or oxygen into the liquid slag.

The process may be operated in a batch-wise manner or continuously in avariety of equipment.

For a batch-wise process, step (1) is achieved most efficiently in ashaft furnace, but can also be performed in a reverberatory, or rotaryfurnace using conventional techniques or in a vessel such as thatdescribed belowfor step (3). Step (2) requires mixing of the liquid slagthus produced with liquid tin-iron alloy. This can be achieved byinjecting gases into a bath containing the liquid slag and hardhead,thereby using the stirring induced by this procedure, or in aconventional rotary furnace. Step (3) requires the removal of tin fromliquid slags to low levels, and therefore requires anew approach, sincethis cannot be achieved using existing techniques. Experiments haveshown that gaseous reductants (which may contain entrained solidreductants) or reducing mixtures of fuel and air and/or oxygen wheninjected into such slags can produce hardhead and a slag for discardhaving a very low tin content. This is preferably carried out in avessel with a deep slag bath, and may, or may not, incorporatepartial-combustion of the reductant to provide the heat required byreactions and heat losses in the system. Thus the batch-wise operationis achievable in a number of ways according to the method of producingconcentrate slag, and reacting this slag with hardhead. The

gaseous reduction operation, step (3), can take place in a rotary, orreverberatory furnace, but a vessel having a deep slag bathis-preferable in order to achieve high efficiency of the reductant used.

Additions of solid carbonaceous reductant to the ini tial charge willgenerally be required in order to produce a non-viscous slag. The slagthus produced is reacted with hardhead and, before tapping the crudemetal product containing less than 2 percent iron, it may or may not beadvantageous to reduce further by injection of reducing gases dependingon the iron to tin ratio in the concentrate. The quantity of reductantrequired in this stage varies from more than that necessary to reduceall of the iron and tin in the concentrate to the ferrous and stannousstates for concentrates with low iron to tin ratios, to less than thatquantity for concentrates with high iron to tin ratios. For example aconcentrate containing 20 wt. percent. tin and 15 wt. percent iron onlyrequired about two-thirds of the quantity of reductant needed to reduceto the stannous and ferrous states, while a concentrate containing 45wt. percent tin and 12 wt. percent iron requires about one andone-quarter times the quantity of reductant needed to reduce to thestannous and ferrous states.

For continuous operation, the process is desirably carried out in avessel comprising suitable regions or zones for achieving the threeprocess steps. For example, in a typical system, melting steps takeplace in a bath situated at the end of a reactor. Here combustible gases(or pulverised coal, or fuel oil) are burnt beneath the slag surfacewith co-injected oxygen containing gases to provide heat for melting.The concentrate and flux may be introduced by dropping them on to thesurface of a pre-existing slag pool or entraining them in the combustiongases.

High tin intermediate slag (iv) flows from the end of the smeltingchamber into a separate region where the gaseous reductant (which maycontain solid carbonaceous material) is injected through a series oflances or tuyeres to produce the tin-iron alloy (ii) and low tin discardslag (v) which is tapped off and discarded. The alloy (ii) flows beneaththe slag layer under gravity towards the concentrate smelting end of thereactor, where iron is removed by reaction with the tin-rich concentrateslag (i) to produce the tin metal product (iii) which is tapped fromthis region, and the intermediate slag (iv) which flows back to thereducing region.

The operation of a continuous tin smelting operation using differentprinciples has been described by Worner (US. Pat. No. 3,634,069, 1972The use of submerged reduction and combination in the present processeliminates the need for a blast furnace to produce hardhead, and leadsto better control of one of the major operating parameters, namely thetin content of discard slag. If a shaft furnace were used in the presentinvention for concentrate smelting, only partial reduction to a low ironmetal would be used and a high tin content slag would be produced.

The feasibility of the process has been investigated in small scaleexperiments in crucibles and also by submerged combustion techniques ina larger reactor. Step (1) may be carried out using conventionalequipment and procedures or by injecting concentrates with fuel and airinto a liquid slag. Step (2) is known to be effective when operated in arotary furnace. In order to investigate the alternative of using gaseousinjection to achieve the necessary mixing, small scale tests wereperformed. For example, hardhead containing 50% iron was reacted with a20% tin concentrate by heating" to produce both phases in the liquidstate and injecting nitrogen. The metal produced contained less than 1%iron. Step (3) was investigated at length using various slags andgaseous reductants and fuels. It was found that slags containing lessthan 2 percent tin were produced in reducing to hardhead at temperaturesbelow l300C. The reduction proceeded at a very fast rate under theconditions studied. Hydrogen, methane and natural gas were found to beeffective. Carbon monoxide injection alone did not result in hardheadproduction, but with entrained brown coal char, hardhead was produced ata similar rate to that for reduction with hydrogen, methane, and naturalgas. The entrainment of a solid carbonaceous reductant withhydrogencontaining or hydrogen-producing gases ensures a high efficiencyof gas utilization when a deep slag bath is used, by maintaining a highpartial pressure of reductant in the gas according to the reactions:

and

co, c 2co 3. Rapid reactions ensure that discard slags are produced withan optimum tin content, depending on the tin-to-iron ratio of theconcentrate.

4. The treatment of liquid hardhead to produce a crude tin product oflow iron content avoids the necessity of coolingand remelting as inconventional practice.

These advantages are particularly important in treating low gradeconcentrates where a large amount of slag is produced for a givenquantity of tin produced. They result in greater plant capacity, lowerlosses of tin in discard slag, less severe conditions for refractories,and lower fuel requirements. These advantages make the processattractive for the treatment of high grade as well as low grade tinconcentrates.

The principles and practice of the present invention are furtherelucidated by the following examples.

EXAMPLE 1 (All parts and percentages are by weight.)

This example illustrates the first two steps of the invention and showsthat the mixing of liquid hardhead with liquid concentrate slag byinjecting a gas is effective in producing crude tin metal of low ironcontent.

A ceramic crucible containing a metal made up from 308g of tin and 30.8gof iron beneath 400 g of a low grade concentrate with 19 percent tin and14% iron was heated to produce liquid phases at 1150C. Nitrogen wasinjected through an alumina tube of diameter 0.25 ins. at l000ml/min for92 minutes, to provide agitation, while the temperature increased from 1150C to 1330C. Samples of the slag obtained by dipping an Inconel rodinto the slag and quenching the rod in water showed a rapid decrease inthe tin content of slag due to reaction with iron in the hardhead. After26 minutes the tin content of the slag remained constant, indicatingthat reaction with the metal had reached equilibrium. The temperature atthis stage was 1260C. After cooling a metal button containing 0.8percent iron was separated from the slag, which contained 8.8 percenttin. The difference between the weight of tin charged in the concentrateand alloy, and the weight of tin obtained in slag and metal indicated aloss of 34 percent of the input tin in fume. The large fume loss wouldbe decreased by injecting nitrogen for the minimum time and restrictingthe temperature of operation.

EXAMPLE 2 This example shows the effectiveness of the gaseous reductionof liquid slag by injection of a hydrogen containing gas to producehardhead and taken together with Example 1 demonstrates the operation ofthe overall process of the invention.

500g of a slag such as that produced in Example 1, containing 8.3percent tin and 24 percent iron was heated in a ceramic crucible to1250C. Natural gas was injected through an alumina tube into the liquidslag thus produced at 1000 ml/min with 0.6g/min of entrained powderedbrown coal char. After 88 minutes of injection hardhead containingpercent iron was produced leaving a slag of tin content 0.95 percent.Percentages of the input tin which reported in the metal, slag, and fumerespectively were 76 percent, and 10 percent, and 14 percent.

EXAMPLE 3 This example shows that the reductants may be partially burntwithin the liquid slag to generate heat without significantly loweringthe rate of reduction in Step 3 of the process.

500g of a slag containing 6 percent tin and 14 percent iron was heatedin a ceramic crucible to 1260C and a mixture of gases comprising methaneat 600 ml/mins and oxygen at 500 ml/min entraining 0.6g/min of powderedbrown coal char injected through an alumina tube. After 63 minutes metalcontaining 23 percent iron and slag containing 0.95 percent tin wereproduced. Percentages of input tin reporting in metal, slag, and fumewere respectively 57 percent, 13 percent and 30 percent.

EXAMPLE 4 This example indicates that gaseous reduction of liquid slagsis effective on a larger scale.

3270g ofa slag containing 6.6% tin and 14% iron was heated in a ceramiccrucible to l3l0C and methane at 2,500 ml/min entraining lg/min browncoal char injected through an alumina tube. In the early stages ofinjection a considerable quantity of slag was lost due to splashing.After 92 minutes metal assaying 42 percent iron and slag containing 0.54percent tin were pro duced. Percentage of input tin reporting in metal,slag, splashed slag and fume were respectively 46 percent, 5 percent, 28percent and 21 percent.

EXAMPLE 5 The example further illustrates steps 1 and 2 of the process.

500 g of slag containing 20% Sn was prepared from a concentrate andfluxes and reacted with g of 50% Sn 50% Fe alloy by bubbling nitrogen at1000 ml per minute through the liquid phases held at 1270C in acrucible. A crude tin metal phase containing 1.4% Fe and a slag phasecontaining 13.4% Sn were produced. Of the tin charged 35% reported inmetal, 44.6% in slag and 20.4% in fume.

EXAMPLE 6 This example shows the operation of the overall process of theinvention in a cyclical batchwise manner. Operation A (Steps 1 and 2)precedes Operation B (Step 3), from which the hard head product isrecycled to Operation C (a further Step 1). The fume generated,consisting of almost pure SnO was treated elsewhere.

OPERATION A 500 g of a tin concentrate containing 49% Sn and 7% Fe weremixed with 89g of calcite and 355 of brown coal char, and heated to1250C in a crucible. g of 50% Sn 50% Fe alloy was added to the melt andnatural gas, at 200 ml/min and air at 1900 ml/min injected through twoconcentric alumina tubes for 40 minutes. 148g of crude tin product,containing 0.54% Fe and 253g of a slag containing 10.4% Sn for furthertreatment were produced.

OPERATION B The slag from Operation A was heated to 1250C and 500 ml/min natural gas entraining 0.3 g/min brown coal char and 3,700 ml/minair were injected through two concentric alumina tubes into the melt for60 minutes. A slag containing 0.8% Sn was produced for discard, togetherwith 40g of tiniron alloy containing 49% Fe for recycle. I

OPERATION C The alloy from Operation B was again added to a meltproduced from 500g of the same concentrate, 89g of calcite, and 35g ofcarbon. 200ml per minute natural gas and 1900 ml/minute air wereinjected into the bath at 1250C for 40 minutes. 150g of crude tin metalproduct containing 0.6% Fe was produced together with 240g of slagcontaining 1 1.4% Sn.

EXAMPLE 7 p This example illustrates smelting of concentrates byinjection with a fuel/air/oxygen mixture into a bath of liquid slag toproduce crude tin metal and subsequent reduction of the high tin slagthus produced to yield a low-tin slag for discard and a tin-iron alloyfor recycle. Smelting A tin concentrate containing 50 percent tin and 7percent iron was mixed with calcite flux and injected, with a reducingcombustion mixture of natural gas, brown coal char, air and oxygen, intoa bath of liquid slag contained in a refractory lined vessel. The vesselwas of cylindrical shape, 0.3 m diameter and contained a slag bath about0.2 m deep.

The fuel/air/oxygen mixture contained about 50% of the oxygen requiredfor complete combustion, the injection rates being as follows:

natural gas 7.7 cfm brown coal char 140 g/min. air 6.5 cfm oxygen 11.3cfm In 45 minutes, 26.3 kg of the concentrate and 1.8 kg of the fluxwere injected through the water-cooled steel lance after which a crudemetal containing 1.1% iron was tapped.

Reduction Injection of the reducing fuel/air/oxygen mixture wascontinued for 53 minutes, without entrainment of concentrate and withthe oxygen flow rate in the mixture lowered to 8.8 cfm thus reducing theoxygen content to about 40 percent of that required for totalcombustion. Finally, a slag containing 1.0 percent tin and a tin-ironalloy containing158% iron was tapped.

EXAMPLE 8 This example illustrates the reduction of a typicalintermediate high-tin slag by injection of a reducing oil- /air/oxygenmixture on a 50 kg scale.

kg of a slag containing 18% tin and 26% iron was mixed with 5 kg ofcalcite and melted to form a liquid slag bath in the vessel of Example7. A reducing combustion mixture of fuel oil, air and oxygen wasinjected into the liquid slag through a water-cooled lance for 59minutes. The fuel/air/oxygen injection rates were as follows: 8n

No. 1 fuel oil 4 Imp. galL/hr.

(emulsified with water) Air 4.5 cfm Oxygen 6.9 cfm This mixture containsabout 44 percent of the oxygen required for complete combustion. (Theaddition of a small amount of water to the oil significantly improvesreduction rates. A few percent of water is sufficient; the above runused 75 ml; i.e., about 4 vol. percent).

The final products tapped from the vessel were a slag containing 1.5percent tin and a metal containing 39 percent iron.

I claim:

1. A method of producing tin from a low grade tin concentratecomprising:

a. melting and partially reducing a mixture of the concentrate and aflux to form a liquid concentrate slag (i) having a Sn content of fromabout 20 percent;

. mixing and reacting the liquid concentrate slag (i) with a liquidtin-iron alloy (ii) having an Fe content of about 10-60 percent toproduce a liquid crude tin metal product (iii) of about 0.1 2 percent Fecontent and a liquid intermediate slag (iv) of about 10 40% Sn content;

. separating the metal product (iii) and the intermediate slag (iv);

. injecting into the liquid intermediate slag (iv) a reducing materialselected from the group consisting of hydrogen, hydrogen-containinggases, hydrogenproducing gases and solid carbonaceous and liquidhydrocarbon materials which on combustion produce such gases to reducethe slag (iv) and reform a molten tin-iron alloy (ii) and a liquiddiscard slag (v) having a Sn content of about 0.5 2 percent;

. separating the alloy (ii) and the discard slag (v);

and recycling the alloy (ii) to the mixing and reacting step.

2. A method as in claim 1, wherein the reducing material injected intothe liquid intermediate slag (iv) is a gas containing an entrained solidcarbonaceous reductant.

3. A method as in claim 2, wherein the solid carbonaceous reductant isbrown coal char.

4. A method as in claim 1, wherein the reducing material is methane ornatural gas.

5. A method as claimed in claim 1, wherein the reducing material is afuel oil.

6. A method as claimed in claim 5, wherein the oil contains added water.

7. A method as in claim 1, wherein the reducing material is partiallyburned within the liquid slag.

8. A method as in claim 1, wherein the temperature of the liquidintermediate slag (iv) being reduced is below '1300C.

9. A method as in claim 1, wherein the mixing of the is carried out byinjection of the concentrate and flux, liquid alloy (ii) and the liquidconcentrate slag (i) is together with fuel and air and/or oxygen belowthe surcarried out by the injection of gases. face of a bath ofconcentrate slag with partial combus- 10. A method as in claim 1,wherein the melting and tion of the fuel. partial reduction of a mixtureof concentrate and flux 5

1. A METHOD OF PROUCING TIN FROM A LOW GRADE TIN CONCENTRATE COMPRISING:A. MELTING AND PARTIALLY REDUCING A MIXTURE OF THE CONCENTRATE AND AFLUX TO FORM A LIQUID CONCENTRATE SLAG (I) HAVING A SN CONTENT OF FROMABOUT 2 - 50 PERCENT, B. MIXING AND REACTING THE LIQUID CONCENTRATE SLAG(I) WITH A LIQUID TIN-ION ALLOY (II) HAVING AN FE CONTENT OF ABOUT 10-60PERCENT TO PRODUCE A LIQUID CRUDE TIN METAL PRODUCT (III) OF ABOUT 0.1I-PERCENT FE CONTENT AD A LIQUID INTERMEDIATE SLAG (IV) OF ABOUT 10 - 40%SN CONTENT, C. SEPARATING THE METAL PRODUCT (III) AND THE INTERMEDIATESLAG (IV), D. INJECTING INTO THE LIQUID INTERMEDIATE SLAG (IV) AREDUCING MATERIAL SELECTED FROM THE GROUP CONSISTING OF HYDROGEN,HYDROGEN-CONTAINING GASES, HYDROGEN-PRODUCING GASES AND SOLIDCARBONACEOUS AND LIQUID HYDROCARBONN MATERIALS WHICH ON COMBUSTIONPRODUCE SUCH GASES TO REDUCE THE SLAG (IV) AND REFORM A MOLTEN TIN-IRONALLOY (III) AND A LIQUID DISCARD SLAG (V) HAVING A SN CONTENT OF ABOUT0.52 PERCENT, E. SEPARATING THE ALLOY (II) AND THE DISCARD SLAG (V), ANDF. RECYCLING THE ALLOY (II) TO THE MIXING AND REACTING STEP.
 2. A methodas iN claim 1, wherein the reducing material injected into the liquidintermediate slag (iv) is a gas containing an entrained solidcarbonaceous reductant.
 3. A method as in claim 2, wherein the solidcarbonaceous reductant is brown coal char.
 4. A method as in claim 1,wherein the reducing material is methane or natural gas.
 5. A method asclaimed in claim 1, wherein the reducing material is a fuel oil.
 6. Amethod as claimed in claim 5, wherein the oil contains added water.
 7. Amethod as in claim 1, wherein the reducing material is partially burnedwithin the liquid slag.
 8. A method as in claim 1, wherein thetemperature of the liquid intermediate slag (iv) being reduced is below1300*C.
 9. A method as in claim 1, wherein the mixing of the liquidalloy (ii) and the liquid concentrate slag (i) is carried out by theinjection of gases.
 10. A method as in claim 1, wherein the melting andpartial reduction of a mixture of concentrate and flux is carried out byinjection of the concentrate and flux, together with fuel and air and/oroxygen below the surface of a bath of concentrate slag with partialcombustion of the fuel.